There was a piece on, I think, the Entertainment Tonight website stating that the series is tanking in the ratings.
They haven't officially put it on the danger list, but in today's climate, if the ratings don't stay consistently high, the suits get all frowny.
What makes all of this so ridiculous is that the show is doing fine in delayed viewing statistics--DVD-R, online viewing, iTunes etc. which is how everyone I personally know tends to watch television.
G.